The ability to produce material patterns on substrates is of substantial industrial importance. In particular, the ability to provide high quality conducting patterns on substrates is essential in the production of circuit boards for the electronics industry. Such patterned substrates also have utility in electrical resistance heating plates, microwave oven doors and a variety of utilitarian and ornamental applications.
In conventional circuit board manufacturing techniques, a continuous metallic foil is typically bonded onto a substrate. However, in some cases, the foil has been substituted by a continuous metallic coating which has been plated or vapor deposited directly on the substrate. A resist is then applied to the substrate in a pattern which defines the desired pattern. The resist generally comprises an organic resin or ink applied through a screen in the desired pattern. A more common processing method, however, uses radiation-sensitive compounds, termed photoresists, which can be imaged or exposed through a suitable patterned mask and then developed. Such photoresists can be of the negative or positive acting type and can be applied as a liquid or a dry film. These photoresists are often of a type which can be developed and stripped using aqueous or organic solvents. The liquid type photoresists are generally applied in a continuous, uniform coating by spraying, roller coating or screen printing.
After developing the photoresist to form a patterned mask, etchants are used to remove exposed metallic material. Subsequently, the remaining mask material is removed. The resulting product is a pattern of metallic material bonded to the substrate surface. At some point prior to, during or subsequent to the patterning process, through-holes are drilled in appropriate locations on the substrate. The interior surfaces of these through-holes are subsequently metallized by any of a variety of known techniques.
The method described above is intended merely to be representative of a variety of different processes, and is not intended to provide an exhaustive description of all currently practised circuit board manufacturing techniques.
Unfortunately, the use of etchants in the formation of patterns upon substrates results in a process having a variety of disdvantages. For example, commonly used etchants can be costly and are typically hazardous in handling and disposal. Additionally, the removal of sections of the metallic material results in etchant attack on the sidewalls of remaining material. This effect, referred to as etch factor, creates difficulties when forming extremely narrow metallic traces on the circuit board, thereby limiting the overall device density on the board. Furthermore, patterning of the substrate using etchants results in the need for a variety of pre- and post-etch process steps, thereby increasing manufacturing time, complexity and scrap rates.
Additionally, the thin foil sheets used in conventional patterning techniques are exceptionally fragile and susceptible to damage. Thus, extreme care must be employed during foil handling and processing. This required care results in additional process complexity and added process costs.
Thus, a need exists for a method for providing layers of pattern material on a substrate in a manner which is efficient, inexpensive and reduces the hazards associated with etchant handling and disposal.